In terms of a merchant account, there are many companies out there to choose from. Amidst the many options, there are a lot of things to be mindful of. I posted a thread previously regarding merchant accounts and what to look out for. You can view it here: http://www.startupnation.com/pages/community/forum_posts.asp ?TID=4393
Like Nikhole said, I have a marketplace listing for an online payment gateway you might want to look at (Authorize.net). (Thanks Nikhole for mentioning me in this thread).
Anyway, if there`s anything I can do to help you or any questions you might have about the merchant account side of the site, please don`t hesitate to ask.
Terence -
Almost a year ago I was in the same position you are now. I was ready to start an e-commerce business and had no idea where to go to get my website, shopping cart, and merchant account taken care of. Since then I now have a website, shopping cart, and merchant account that are functional, easy to use and to which I give a lot of credit to the succes of my search engine rankings and success of my growing business at www.BoxerHaus.com It has only been 9 months now since my online store went live.
I feel very fortunate to have located a wonderful and affordable web designer at All Medianet www.allmedianet.com My web design came with a great shopping cart - Apple Cart from Spads.com www.spads.com The direct link to the Apple Cart information is http://www.spads.com/applecartdb.html I also set up my merchant account through Spads and I use Authorize.net and I do have competitive merchant rates. I have wonderful customer service from all of these services and they were affordable compared to other estimates I had gathered.
I also wanted a store where I had control of editing products, categories, front page featured products, etc. With AllMedianet and my Apple Cart I have the freedom to do all of these things and I am not locked in with someone who charges me every time I want a change with store product management or on whom I have to wait to make these changes.
Better than affordable and ease of use, Apple Cart has a design that the search engines love! It appears the search engines are loving the Javascript in the cart and it did not take my business long to start climbing quickly in search engine rankings considering it was a new online business AND the fact that I have not spent one penny on search engine submissions, packages, etc.
Yahoo and MSN Live especially love the Apple Cart:
- Currently if you go to these engines and run a search for Boxer Dog Gifts, my store ranks as follows: #2 at Live, #5 at Yahoo and #13 at Google, again with no paid search engine submissions.
- Search these engines for Boxer Gifts and BoxerHaus.com ranks: #2 at Yahoo, #10 at Live, and #25 at Google.
- Search for Boxer Dog Merchandise and Boxer Haus results are: #2 at Yahoo, #3 at Live, and #10 at Google.
Another interesting fact that was noted recently is the search engines are also indexing the additional categories from the store templates. Not sure why this is happening but I am certainly not complaining.
TJ Graff of www.GoTruckStop.com who also uses the Apple Cart noticed this had occurred when he asked a customer who purchased a truck accessory from him how they located him. They advised by a search engine listing at Yahoo. TJ discovered that the only key word in that search phrase for that product could have only come from the addtional product category.
Recently Apple Cart made new changes where the front page can feature product that will change every time you refresh your screen or come back to the page again. This way the front page featured products is always changing and the customer is able to view fresh product immediately every time they go to the front page of the store. BoxerHaus.com has not been indexed yet since this new change took place so it will be interesting to see what happens with the rankings once I am indexed again which should be soon.
If you are looking for a shopping cart that is easy to use and works well with the search engines and that you have control over and is not another "me too" shopping cart I personally highly recommend Apple Cart. The fact it is affordable is an added bonus.
I know I probably sound like an Apple Cart commercial (perhaps they should hire me! LOL!) but I can`t express more how satisfied I am with how the cart and web design has worked for my store and how nice it is to have the freedom to manage it myself as well. And there is no doubt that my search engine rankings are credited to the Apple Cart design. 
Has anyone ever used Storefront (http://www.storefront.net/default.asp?REFERER=Ropelato) shopping cart software? If so, what do you think. I`m heavily evaluating different options.
Thanks